It is now possible to determine the location of a mobile electronic device using the Global Positioning System (GPS), or triangulation using receive signal strength from mobile telephone cellular towers or previously mapped radio frequency (RF) transmitters, such wireless access points. Location coordinates from GPS signals can be accurate to within several meters, but the signals are often not available indoors. RF triangulation techniques might have accuracy on the order of 1-25 meters, but can also be off by 100 meters or more in some cases.